In flow control valves a specific device is utilized as the flow-controlling element, and may be provided in many different forms. The flow-control element may be directly actuated manually, or by any other suitable indirect or powered means, and is positioned inside the valve so that the flow of fluids and gases (hereafter generally “fluids”) can be modulated according to various application-specific requirements. In operation, the flow control element is subjected to forces and moments from the fluids. These fluid forces and moments are a function of fluid pressure and flow rate. Actuation forces and moments must therefore overcome the fluid forces and moments in order to allow control valves to modulate flow effectively. Control valves may greatly benefit from flow controlling elements, a valve ball for instance, configured to reduce the fluid forces and moments that the fluid exerts on the flow controlling element.
Inherent to conventional ball valve designs is a tendency for the ball to change position (i.e., “drift”) when the ball is placed in some “throttled” position between fully open and fully closed. One way to overcome this tendency is to provide friction between the ball and a complementary mating surface of a valve housing or body, called a “seat,” to maintain the valve ball in a desired position. Likewise, friction in a valve manual control handle assembly, and hydraulic forces internal to the valve ball, may be utilized to provide the valve assembly with the capability to maintain the valve ball position in select fluid-flow positions. In a properly functioning valve, the frictional forces are sufficient to resist the unbalanced hydraulic forces of the fluid. An exemplary design is set forth in U.S. Pat. No. 6,173,940 to Kardohely, et al.
The flow control element is also subjected to friction forces from other associated fixed or movable valve elements so that the friction forces resist the fluid forces and moments, allowing for stable control of the flow controlling element position upon actuation. These friction forces, however, also aid to define the required operating forces and moments for the valve and, if not optimized for a certain flow, may render the flow controlling element difficult if not impossible to operate. The solution is not simply to reduce friction in the valve, since reducing the friction would likely result in undesirable drifting of the ball position. There is thus a need for a ball valve that is easily adjustable, yet not having a tendency to drift.